(a) Field of Invention
The present invention relates to an improved noise damping guard for a circular saw blade and wherein the guard walls are constructed of a sandwich material mounted in parallel relationship to each side of the blade and defining an air gap between the guard and the blade whereby to dampen blade vibration and noise and to substantially reduce blade heating when occasionally in frictional contact with the guard.
(b) Description of the Prior Art
In the prior art, such as in U.S. Pat. No. 4,137,806, there is disclosed a silencing mechanism for circular saws. The mechanism comprises a casing made of plastics and foam material whereby to absorb noise caused by a saw blade. The material utilized to effect such noise absorption is a foam material supported in a structural plastics guard frame. As disclosed in the patent, such guard was found to achieve noise reduction on 14, 16, and 18 inch blades, with the maximum noise reduction obtained being in the range of 10 to 11.4 db. However, the disadvantage of this noise damping guard is that when the blade vibrates or is forced to touch the side walls, the side walls will self-destruct or be severely damaged and the blade will heat up due to its contact with such vinyl-like material.
Heating of the blade, when in operation, also tends to soften the foam-like material and causes the retention and thus the build-up of sawdust between the saw blade and the side walls. This results in reducing the noise effectiveness of the silencing mechanism and in increased maintenance and repair to the guard and renders the saw inoperative. Often it is necessary to replace the guard if excessive wear is resulted from its contact with the vibrating saw blade.
It is a well known fact that noise in a saw blade is caused in large part by the vibrations in the blade. Due to the structural nature of the noise mechanism of the above prior art, the blade vibrations cannot be reduced effectively and noise attenuations is achieved primarily through the absorption characteristics of the foam-like material. Another major disadvantage, results from the potential damage or destruction of the noise mechanism walls if a piece of hard material happens to be forced or squeezed in the gap between the saw blade and the guard.